posix_acl: Clear SGID bit when setting file permissions

When file permissions are modified via chmod(2) and the user is not in
the owning group or capable of CAP_FSETID, the setgid bit is cleared in
inode_change_ok().  Setting a POSIX ACL via setxattr(2) sets the file
permissions as well as the new ACL, but doesn't clear the setgid bit in
a similar way; this allows to bypass the check in chmod(2).  Fix that.

References: CVE-2016-7097
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>

diff --git a/fs/9p/acl.c b/fs/9p/acl.c
index 5b6a174..b3c2cc7 100644 (file)
--- a/fs/9p/acl.c
+++ b/fs/9p/acl.c
@@ -276,32 +276,26 @@ static int v9fs_xattr_set_acl(const struct xattr_handler *handler,
        switch (handler->flags) {
        case ACL_TYPE_ACCESS:
                if (acl) {
-                       umode_t mode = inode->i_mode;
-                       retval = posix_acl_equiv_mode(acl, &mode);
-                       if (retval < 0)
+                       struct iattr iattr;
+
+                       retval = posix_acl_update_mode(inode, &iattr.ia_mode, &acl);
+                       if (retval)
                                goto err_out;
-                       else {
-                               struct iattr iattr;
-                               if (retval == 0) {
-                                       /*
-                                        * ACL can be represented
-                                        * by the mode bits. So don't
-                                        * update ACL.
-                                        */
-                                       acl = NULL;
-                                       value = NULL;
-                                       size = 0;
-                               }
-                               /* Updte the mode bits */
-                               iattr.ia_mode = ((mode & S_IALLUGO) |
-                                                (inode->i_mode & ~S_IALLUGO));
-                               iattr.ia_valid = ATTR_MODE;
-                               /* FIXME should we update ctime ?
-                                * What is the following setxattr update the
-                                * mode ?
+                       if (!acl) {
+                               /*
+                                * ACL can be represented
+                                * by the mode bits. So don't
+                                * update ACL.
                                 */
-                               v9fs_vfs_setattr_dotl(dentry, &iattr);
+                               value = NULL;
+                               size = 0;
                        }
+                       iattr.ia_valid = ATTR_MODE;
+                       /* FIXME should we update ctime ?
+                        * What is the following setxattr update the
+                        * mode ?
+                        */
+                       v9fs_vfs_setattr_dotl(dentry, &iattr);
                }
                break;
        case ACL_TYPE_DEFAULT:

diff --git a/fs/btrfs/acl.c b/fs/btrfs/acl.c
index 53bb7af..247b8df 100644 (file)
--- a/fs/btrfs/acl.c
+++ b/fs/btrfs/acl.c
@@ -79,11 +79,9 @@ static int __btrfs_set_acl(struct btrfs_trans_handle *trans,
        case ACL_TYPE_ACCESS:
                name = XATTR_NAME_POSIX_ACL_ACCESS;
                if (acl) {
-                       ret = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (ret < 0)
+                       ret = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (ret)
                                return ret;
-                       if (ret == 0)
-                               acl = NULL;
                }
                ret = 0;
                break;

diff --git a/fs/ceph/acl.c b/fs/ceph/acl.c
index 4f67227..d0b6b34 100644 (file)
--- a/fs/ceph/acl.c
+++ b/fs/ceph/acl.c
@@ -95,11 +95,9 @@ int ceph_set_acl(struct inode *inode, struct posix_acl *acl, int type)
        case ACL_TYPE_ACCESS:
                name = XATTR_NAME_POSIX_ACL_ACCESS;
                if (acl) {
-                       ret = posix_acl_equiv_mode(acl, &new_mode);
-                       if (ret < 0)
+                       ret = posix_acl_update_mode(inode, &new_mode, &acl);
+                       if (ret)
                                goto out;
-                       if (ret == 0)
-                               acl = NULL;
                }
                break;
        case ACL_TYPE_DEFAULT:

diff --git a/fs/ext2/acl.c b/fs/ext2/acl.c
index 42f1d18..e725aa0 100644 (file)
--- a/fs/ext2/acl.c
+++ b/fs/ext2/acl.c
@@ -190,15 +190,11 @@ ext2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
                case ACL_TYPE_ACCESS:
                        name_index = EXT2_XATTR_INDEX_POSIX_ACL_ACCESS;
                        if (acl) {
-                               error = posix_acl_equiv_mode(acl, &inode->i_mode);
-                               if (error < 0)
+                               error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                               if (error)
                                        return error;
-                               else {
-                                       inode->i_ctime = CURRENT_TIME_SEC;
-                                       mark_inode_dirty(inode);
-                                       if (error == 0)
-                                               acl = NULL;
-                               }
+                               inode->i_ctime = CURRENT_TIME_SEC;
+                               mark_inode_dirty(inode);
                        }
                        break;
 

diff --git a/fs/ext4/acl.c b/fs/ext4/acl.c
index c6601a4..dfa5199 100644 (file)
--- a/fs/ext4/acl.c
+++ b/fs/ext4/acl.c
@@ -193,15 +193,11 @@ __ext4_set_acl(handle_t *handle, struct inode *inode, int type,
        case ACL_TYPE_ACCESS:
                name_index = EXT4_XATTR_INDEX_POSIX_ACL_ACCESS;
                if (acl) {
-                       error = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (error < 0)
+                       error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (error)
                                return error;
-                       else {
-                               inode->i_ctime = ext4_current_time(inode);
-                               ext4_mark_inode_dirty(handle, inode);
-                               if (error == 0)
-                                       acl = NULL;
-                       }
+                       inode->i_ctime = ext4_current_time(inode);
+                       ext4_mark_inode_dirty(handle, inode);
                }
                break;
 

diff --git a/fs/f2fs/acl.c b/fs/f2fs/acl.c
index 4dcc9e2..3134424 100644 (file)
--- a/fs/f2fs/acl.c
+++ b/fs/f2fs/acl.c
@@ -210,12 +210,10 @@ static int __f2fs_set_acl(struct inode *inode, int type,
        case ACL_TYPE_ACCESS:
                name_index = F2FS_XATTR_INDEX_POSIX_ACL_ACCESS;
                if (acl) {
-                       error = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (error < 0)
+                       error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (error)
                                return error;
                        set_acl_inode(inode, inode->i_mode);
-                       if (error == 0)
-                               acl = NULL;
                }
                break;
 

diff --git a/fs/gfs2/acl.c b/fs/gfs2/acl.c
index 363ba9e..2524807 100644 (file)
--- a/fs/gfs2/acl.c
+++ b/fs/gfs2/acl.c
@@ -92,17 +92,11 @@ int __gfs2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
        if (type == ACL_TYPE_ACCESS) {
                umode_t mode = inode->i_mode;
 
-               error = posix_acl_equiv_mode(acl, &mode);
-               if (error < 0)
+               error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+               if (error)
                        return error;
-
-               if (error == 0)
-                       acl = NULL;
-
-               if (mode != inode->i_mode) {
-                       inode->i_mode = mode;
+               if (mode != inode->i_mode)
                        mark_inode_dirty(inode);
-               }
        }
 
        if (acl) {

diff --git a/fs/hfsplus/posix_acl.c b/fs/hfsplus/posix_acl.c
index ab7ea25..9b92058 100644 (file)
--- a/fs/hfsplus/posix_acl.c
+++ b/fs/hfsplus/posix_acl.c
@@ -65,8 +65,8 @@ int hfsplus_set_posix_acl(struct inode *inode, struct posix_acl *acl,
        case ACL_TYPE_ACCESS:
                xattr_name = XATTR_NAME_POSIX_ACL_ACCESS;
                if (acl) {
-                       err = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (err < 0)
+                       err = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (err)
                                return err;
                }
                err = 0;

diff --git a/fs/jffs2/acl.c b/fs/jffs2/acl.c
index bc2693d..2a0f2a1 100644 (file)
--- a/fs/jffs2/acl.c
+++ b/fs/jffs2/acl.c
@@ -233,9 +233,10 @@ int jffs2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
        case ACL_TYPE_ACCESS:
                xprefix = JFFS2_XPREFIX_ACL_ACCESS;
                if (acl) {
-                       umode_t mode = inode->i_mode;
-                       rc = posix_acl_equiv_mode(acl, &mode);
-                       if (rc < 0)
+                       umode_t mode;
+
+                       rc = posix_acl_update_mode(inode, &mode, &acl);
+                       if (rc)
                                return rc;
                        if (inode->i_mode != mode) {
                                struct iattr attr;
@@ -247,8 +248,6 @@ int jffs2_set_acl(struct inode *inode, struct posix_acl *acl, int type)
                                if (rc < 0)
                                        return rc;
                        }
-                       if (rc == 0)
-                               acl = NULL;
                }
                break;
        case ACL_TYPE_DEFAULT:

diff --git a/fs/jfs/acl.c b/fs/jfs/acl.c
index 21fa92b..3a1e155 100644 (file)
--- a/fs/jfs/acl.c
+++ b/fs/jfs/acl.c
@@ -78,13 +78,11 @@ static int __jfs_set_acl(tid_t tid, struct inode *inode, int type,
        case ACL_TYPE_ACCESS:
                ea_name = XATTR_NAME_POSIX_ACL_ACCESS;
                if (acl) {
-                       rc = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (rc < 0)
+                       rc = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (rc)
                                return rc;
                        inode->i_ctime = CURRENT_TIME;
                        mark_inode_dirty(inode);
-                       if (rc == 0)
-                               acl = NULL;
                }
                break;
        case ACL_TYPE_DEFAULT:

diff --git a/fs/ocfs2/acl.c b/fs/ocfs2/acl.c
index 2162434..164307b 100644 (file)
--- a/fs/ocfs2/acl.c
+++ b/fs/ocfs2/acl.c
@@ -241,13 +241,11 @@ int ocfs2_set_acl(handle_t *handle,
        case ACL_TYPE_ACCESS:
                name_index = OCFS2_XATTR_INDEX_POSIX_ACL_ACCESS;
                if (acl) {
-                       umode_t mode = inode->i_mode;
-                       ret = posix_acl_equiv_mode(acl, &mode);
-                       if (ret < 0)
-                               return ret;
+                       umode_t mode;
 
-                       if (ret == 0)
-                               acl = NULL;
+                       ret = posix_acl_update_mode(inode, &mode, &acl);
+                       if (ret)
+                               return ret;
 
                        ret = ocfs2_acl_set_mode(inode, di_bh,
                                                 handle, mode);

diff --git a/fs/orangefs/acl.c b/fs/orangefs/acl.c
index 28f2195..7a37544 100644 (file)
--- a/fs/orangefs/acl.c
+++ b/fs/orangefs/acl.c
@@ -73,14 +73,11 @@ int orangefs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
        case ACL_TYPE_ACCESS:
                name = XATTR_NAME_POSIX_ACL_ACCESS;
                if (acl) {
-                       umode_t mode = inode->i_mode;
-                       /*
-                        * can we represent this with the traditional file
-                        * mode permission bits?
-                        */
-                       error = posix_acl_equiv_mode(acl, &mode);
-                       if (error < 0) {
-                               gossip_err("%s: posix_acl_equiv_mode err: %d\n",
+                       umode_t mode;
+
+                       error = posix_acl_update_mode(inode, &mode, &acl);
+                       if (error) {
+                               gossip_err("%s: posix_acl_update_mode err: %d\n",
                                           __func__,
                                           error);
                                return error;
@@ -90,8 +87,6 @@ int orangefs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
                                SetModeFlag(orangefs_inode);
                        inode->i_mode = mode;
                        mark_inode_dirty_sync(inode);
-                       if (error == 0)
-                               acl = NULL;
                }
                break;
        case ACL_TYPE_DEFAULT:

diff --git a/fs/posix_acl.c b/fs/posix_acl.c
index 59d47ab..bfc3ec3 100644 (file)
--- a/fs/posix_acl.c
+++ b/fs/posix_acl.c
@@ -626,6 +626,37 @@ no_mem:
 }
 EXPORT_SYMBOL_GPL(posix_acl_create);
 
+/**
+ * posix_acl_update_mode  -  update mode in set_acl
+ *
+ * Update the file mode when setting an ACL: compute the new file permission
+ * bits based on the ACL.  In addition, if the ACL is equivalent to the new
+ * file mode, set *acl to NULL to indicate that no ACL should be set.
+ *
+ * As with chmod, clear the setgit bit if the caller is not in the owning group
+ * or capable of CAP_FSETID (see inode_change_ok).
+ *
+ * Called from set_acl inode operations.
+ */
+int posix_acl_update_mode(struct inode *inode, umode_t *mode_p,
+                         struct posix_acl **acl)
+{
+       umode_t mode = inode->i_mode;
+       int error;
+
+       error = posix_acl_equiv_mode(*acl, &mode);
+       if (error < 0)
+               return error;
+       if (error == 0)
+               *acl = NULL;
+       if (!in_group_p(inode->i_gid) &&
+           !capable_wrt_inode_uidgid(inode, CAP_FSETID))
+               mode &= ~S_ISGID;
+       *mode_p = mode;
+       return 0;
+}
+EXPORT_SYMBOL(posix_acl_update_mode);
+
 /*
  * Fix up the uids and gids in posix acl extended attributes in place.
  */

diff --git a/fs/reiserfs/xattr_acl.c b/fs/reiserfs/xattr_acl.c
index dbed42f..2737668 100644 (file)
--- a/fs/reiserfs/xattr_acl.c
+++ b/fs/reiserfs/xattr_acl.c
@@ -242,13 +242,9 @@ __reiserfs_set_acl(struct reiserfs_transaction_handle *th, struct inode *inode,
        case ACL_TYPE_ACCESS:
                name = XATTR_NAME_POSIX_ACL_ACCESS;
                if (acl) {
-                       error = posix_acl_equiv_mode(acl, &inode->i_mode);
-                       if (error < 0)
+                       error = posix_acl_update_mode(inode, &inode->i_mode, &acl);
+                       if (error)
                                return error;
-                       else {
-                               if (error == 0)
-                                       acl = NULL;
-                       }
                }
                break;
        case ACL_TYPE_DEFAULT:

diff --git a/fs/xfs/xfs_acl.c b/fs/xfs/xfs_acl.c
index b6e527b..8a0dec8 100644 (file)
--- a/fs/xfs/xfs_acl.c
+++ b/fs/xfs/xfs_acl.c
@@ -257,16 +257,11 @@ xfs_set_acl(struct inode *inode, struct posix_acl *acl, int type)
                return error;
 
        if (type == ACL_TYPE_ACCESS) {
-               umode_t mode = inode->i_mode;
-               error = posix_acl_equiv_mode(acl, &mode);
-
-               if (error <= 0) {
-                       acl = NULL;
-
-                       if (error < 0)
-                               return error;
-               }
+               umode_t mode;
 
+               error = posix_acl_update_mode(inode, &mode, &acl);
+               if (error)
+                       return error;
                error = xfs_set_mode(inode, mode);
                if (error)
                        return error;

diff --git a/include/linux/posix_acl.h b/include/linux/posix_acl.h
index d5d3d74..bf1046d 100644 (file)
--- a/include/linux/posix_acl.h
+++ b/include/linux/posix_acl.h
@@ -93,6 +93,7 @@ extern int set_posix_acl(struct inode *, int, struct posix_acl *);
 extern int posix_acl_chmod(struct inode *, umode_t);
 extern int posix_acl_create(struct inode *, umode_t *, struct posix_acl **,
                struct posix_acl **);
+extern int posix_acl_update_mode(struct inode *, umode_t *, struct posix_acl **);
 
 extern int simple_set_acl(struct inode *, struct posix_acl *, int);
 extern int simple_acl_create(struct inode *, struct inode *);